The present invention relates to a hot seal seam forming apparatus for forming a plurality of laterally spaced thermal seams in a continuously moving pliable web and particularly to the forming of the hem seals in a draw tape bag.
Plastic and like webs are processed in high speed automated machines to form various products. A draw tape bag forming apparatus is disclosed in the copending application Ser. No. 158,418 of Robert J. Wech entitled Draw Tape Bag Forming Method and Apparatus, filed on even date herewith and assigned to a common assignee herewith In forming the draw tape bag from a flat plastic web, the web has the edges folded to form the hem. The hem is sealed by passing the folded edge over a sealing drum having concentrated circumferential heat lines aligned with the inner edge portion of the hems. In passing over the heating drum, the seam is continuously formed in the continuously uninterrupted moving web. A practical seal unit is shown in U.S. Pat. No. 4,664,649 which issued May 12, 1987 wherein a drum is provided with a tape strip on the drum face aligned with the desired seal location. The tape strip stretches and raises the hemmed web as it moves over the taped drum. Semi-circular hot air nozzle units are aligned one each with each tape strip. Each nozzle unit generates a continous blast of hot air directed onto the drum and the web passing there between. The hot air rapidly causes the web to melt or become molten and forms a line weld seam in alignment with the tape strip. In the high speed forming of draw tape bags, the precise alignment of the folded hem is difficult to maintain. Further, different width bags require adjustment of the tape strips on the drum. The tape strip is releasably secured to the drum face to permit location on the drum in accordance with the location of the hems and particularly the hem seal lines. The adjustment of the tape strip requires shut down of the machine.
The positioning of the small narrow tape, even in an initial set up may require two or more attempts to properly align the narrow tape strips for system optimum operation. Although the hem size can be enlarged to allow for normal web tolerances, other factors are often adversely effected in a draw tape bag area. For example, if the hem size is enlarged, the positioning of the tape strip can vary with respect to each other and results in some misalignment. This effects the strength of the bond between the straps and the bag elements with a consequent variation in the overall carrying ability of the draw tape bag. The tape strip material of course may also be frequently discarded during a repositioning setup or adjustment, resulting in not only excessive down time but strip and bag scrap.
Although the initial set up can be provided in a reasonable fashion, the necessity of slight adjustment during a run often arises. To shut down the machine at that time is not only costly but inconvenient.
There is a demand and need for a more cost and time efficient apparatus for adjusting the alignment of the heat seal unit and the web.